ABOVE: Striped Treeshrew illustration from  the Phillipps Guide to the Mammals of Borneo by Karen Phillipps. Rhinarium drawings from Lyon (1913) A Monograph of the Treeshrews
BELOW: All photos taken by Arlene Walshe  in Temburong, Brunei. These photos clearly show a treeshrew with an extended rhinarium a  triangular patch of bare skin contiguous with the bare nose of the treeshrew. According to Lyon (1913) this means that this treeshrew can only be either Striped Treeshew  Tupaia dorsalis or Large Treeshrew Tupaia tana.
A close look at the photos below shows that the claws of the front feet are very large and prominent- which is a characteristic of Tupaia tana NOT Tupaia dorsalis
However, the black striped down the center of the back appears to extend almost to the base of the tail. This is a characteristic of Tupaia dorsalis NOT Tupaia tana.

In addition  the treeshrew in the photograph has a reddish tip to the tail which is a characteristic of the locally common Brunei treeshrew Tupaia picta.  T. picta also has a stripe down the back similar to that on T. doralis.

Tupaia tana is extremely variable in appearance in different areas of Borneo. All treeshrews have a tendency to mimic other species of small mammals so my guess is that the superficial appearance of the coat  can be ignored which means that this can only be the Brunei race of Tupaia tana based on the very distinctive large front claws and the extended rhinarium.